U.S. Pat. No. 4,569,792 is directed to novel compounds available by conversion from human proinsulin. One of these compounds, designated des (64,65)-human proinsulin [des(64,65)HPI], has the following structure: ##STR1## The foregoing compound differs from human proinsulin by removal of amino acids 64 and 65 with a resultant two-chain molecule joined by disulfide bonds in a manner analogous to that of human insulin.
The molecule exhibits insulin-like activity and, thus, is useful in the treatment of diabetes.
Des(64,65)HPI, as described in U.S. Pat. No. 4,569,792, was prepared in a two-step reaction sequence from human proinsulin (HPI). The human proinsulin was first treated with trypsin to produce, among others, (65-A1 split)HPI. Purified (65-A1 split)HPI treated with carboxypeptidase B yielded the desired des(64,65)HPI.
In Given et al., J. Clin. lnvest. 76, 1398-1405 (1985), a one-step process is described for producing des(64,65)HPI from HPl. The process involves treating HPI with trypsin and carboxypeptidase B in the presence of Tris buffer at pH 7.5 at 22.degree. C.(page 1399, column 1). This process resulted in formation of des(3l,32)HPI in about a 3:1 ratio relative to des(64,65)HPI (page 1400, column 2).
A very efficient and facile method for producing des(64,65)HPI has now been discovered. This method permits a one-step conversion of human proinsulin to des(64,65)HPl in high yield. In carrying out the process of this invention, any or all of a number of parameters are employed.